Relationships between gonad development and sex steroids level at different age of Acipenser schrenckii

Amur sturgeon Acipenser schrenckii was distributed in Heilongjiang River. With the gradual perfection of culture technique, Acipenser schrenckii had been a new species in terms of aquaculture. The culture yields have increased gradually. Some scientists have worked on some relative studies such as artificial propagation, embryonic and larval development and histological observations of digestive system. But no substantial information is available on gonad and related sex steroids for Amur sturgeon. The gonad development at all stages were influenced by sex steroid hormone. Study on sex steroid level in serum can provide new information on the testicular and ovarian steroidogenic capacity of sturgeon, and may serve as the basis for further studies on the hormonal control of male and female gonadal development in this fish. The present study deals with the results of histological observations on the gonad development and the serum sex steroids levels from 1 to 5 years of age and the stocks were also examined, to obtain preliminary information on endocrine control of gonad development and elucidate the most suitable time for induction of artificial propagation. In May 2002,the fish used in this study at 1 to 5 years of age were stocked and raised in outdoor cement pool in the Technological and Engineering Center of Sturgeon’s Reproduction , Beijing, China, under natural water temperature and day length. The lowest monthly average water temperature was 6 ℃ in December and 4 ℃in February, and the highest was 24 ℃ in June and 28 ℃ in August. The longest day time was 13.5 h (June) and the shortest was 9 h (December). The fish were fed commercial sturgeon food. The fragments of testes and ovarian, both from 1-to 5-year-old fish, were collected randomly by biopsy. Portions of gonad, from approximately the same area in the middle part of the organs, were removed through a surgical incision 5-8 cm long laterally on the abdomen. The blood was collected from the caudal vein of each fish. The gonad development stage was determined by light microscopy according to Детлаф and SUN.The gonad fragments were fixed in Bouin’s solution for 48 h, and embedded in cytoparaffin after dehydration and clearing. Serial sections of 4-7 μm thickness were stained with Delafield’s haematoxylin and eosin. The levels of testosterone (T) and estradiol-17β (E_2) were measured by radioimmunoassays (RIA) according to Simpon and Wright. The results showed that: at age 1, which was the early stage of sex differentiation, the levels of testosterone (T) and 17β-estradiol (E_2) were (1.8±0.724) nmol/L(α=0.01) and ( 50.3±2.879) pmol/L(α=0.05), respectively. At age 2, the testes were at stageⅡand the ovarian was at stage I when the levels of T and E_2 were (2.2±0.934) nmol/L (α=0.01) and (38.9±2.343 )pmol/L(α=0.05), respectively. At age 3, the testes were at stage Ⅲ and the ovarian was at stage I, and the levels of T and E_2 were (9.6±1.936) nmol/L (α=0.05)and (44.8±2.605) pmol/L (α=0.05), respectively. At age 4, the testes were at stage Ⅲ and the ovarian at stageⅡwhen T and E_2 levels were (26.3±2.105) nmol/L (α=0.05) and (55.3±3.053) pmol/L (α=0.05), respectively. At age 5, the testes were mature and the ovarian were at stage Ⅲ when the levels of T and E_2 were (13.9±1.652) nmol/L(α=0.05) and (137.7±5.880) pmol/L (α=0.05),respectively.The levels of T and E_2 were 40.5-74.6 nmol/L and 56-116 pmol/L, respectively, in the male stocks, and 39.7-73.2 nmol/L and 544-904 pmol/L in the female stocks, respectively.